Segmented bias roll

ABSTRACT

A bias roll xerographic transfer system for simultaneous single pass duplex copying is disclosed. The transfer roll is provided with multiple, discrete (segmented), conductive areas. In the transfer nip area the transfer bias potential is applied through a sliding contact to only the conductive segments which are in that area. A grounding brush contacts different conductive segments in separate image charging and cleaning areas, both spaced from the transfer nip. The surface of the transfer roll, with a toner image thereon, is independently corona charged in the image charging area. Thus, the transfer and image charging functions are independent. The image charging corona means may be switched between D.C. and A.C. outputs in response to movement of the transfer roll to effect image reversal or neutralization, respectively.

[451 Nov. 12, 1974 v United States Patent [1 1 Young SEGMENTED BIAS ROLLABSTRACT Inventor: Eugene F. Young, Henrietta, NY.

A bias roll xerographic transfer system for simulta- Assignee: XeroxCorporation, Stamford,

Conn.

Dec. 17, 1973 [22] Filed:

Appl. No.: 425,417

that area. A grounding brush contacts different conductive segments inseparate image charging and cleaning areas, both spaced from thetransfer nip. The surface of the transfer roll, with a toner image 66fiw 4 31 mmm 5 W c Ur Una e "ms L l WM k UmF nH o o 555 ill thereon, isindependently corona charged in the image charging area. Thus, thetransfer and image charging functions are independent. The imagecharging corona means may be switched between DC and AC. out- [56]References Cited UNITED STATES PATENTS- puts in response to movement ofthe transfer roll to 1 effect image reversal orneutralization,respectively.

Primary Examiner-John M. Horan 6 Claims, 1 Drawing Figure SEGMENTED BIASROLL The present invention relates to an electrostatographic duplexcopying system with a transfer system providing image transfer biasingindependently of imaging biasing.

In a conventional transfer station in xerography, a developed image oftoner particles (from the image developer material) is transferred froma photoreceptor (the imaging surface) to a cut or roll fed copy sheet(the final image support surface), either directly or after anintermediate image transfer to an intermediate surface. Such imagetransfers'are also required in other electrostatographic processingsystems, such as electrophoretic development/In TESI systems theintermediately transferred image may be an undeveloped latentelectrostatic image;

Transfer is most commonly achieved by applying electrostatic forcefields in a transfer nip sufficient to overcome the forces holding thetoner to its original support surface and to attract most of the tonerto transfer over onto the contacting second surface. These 2,807,233, orby a D.C. biased transfer roller or belt rolling along the back of thecopy sheet. Examples of bias roller transfer systems are described inallowed U.S. Pat. application Ser. No. 309,562, filed Nov. 24, 1972, byThomas .Meagher, and in U.S. Pat. Nos. 2,807,233; 3,043,684; 3,267,840;3,328,193; 3,598,580; 3,625,146{ 3,630,591; 3,691,993; 3,702,482; and3,684,364.

The difficulties of successful image transfer are well known. In thepre-transfer(pre-nip) region, before the copy paper contacts the image,if the transfer fields are high the image is susceptible to prematuretransfer, across the air gap, leading to decreased resolution or fuzzyimages. Further, if there is ionization in the prenip air gap from highfields, it may lead to strobing or other image defects, lossfof transferefficiency, and a lower latitude of system operating parameters. Yet, inthe directly adjacent nip region itself the transfer field should belarge as possible (greater than approximately volts per micron) toachieve high transfer efficiency.

and stable transfer. In the next adjacent post-nip region, at thephotoconductor/copy sheet separation area, if the transfer fields aretoo low hollow characters may be generated. On the other hand,improperionization in the post-nip region may cause image instability or copysheet detacking problems Variations in ambient conditions, copy paper,contaminents, etc., can all affect the necessary transfer parameters. Toachieve these differenttransfer field parameters consistently, and withappropriate transitions, is dlfficult even for simplex (single sideimage) copies. Duplex (both sides) copying presents much greatertransfer difficulties, particularly' where the two images aretransferred simultanteously to the opposing sides of the copy sheet asdisclosed here.

Some exemplary duplexelectrostatographic copying systems are disclosedin the following U.S. Pat. Nos. 3,506,347 to C. F. Carlson, issued Apr.14, 1970; 3,671,118 to J. Fantuzzo et-al., issued June 20, 1972;3,672,765 to C. Altmann, issued June 27, 1972; 3,687,541 to G. A. Aseret al., issued Aug. 29, 1972,

2 and 3,697,171 to W.-A. Sullivan, issued Oct. 10, 1972.

The Sullivan U.S. Pat. No. 3,697,171 is of particular interest asdisclosing details of the type of simultaneous duplex transfer systemdisclosed in the present specification embodimcnt, as well as thegeneral requirements and theory of such a system. Accordingly, thispatent is specifically made a part of this specification. This Sullivanpatent, for example, teaches corona discharge polarity reversal of afirst toner image (which has been intermediately transferred to thetransfer roller surface) at a corona charging position spaced from thetransfer nip, and subsequent simultaneous transfer to opposite sides ofa copy sheet of the first toner image with a second toner image on thephotoreceptor. The present invention represents an improvement over thisdisclosed system.

Another referenceof particular interest is U.S. Pat. No. 3,684,364,issued Aug. 15, 1972, to Fred W. Schmidlin. This patent teaches axerographic roller electrode transfer system in which appropriatetransfer potential can be provided to the roller from a transfer biassource through a plurality of fixed contacts. These contacts slidablyengage moving segmented conductors mounted inside the roller, spacedaround the circumference of the roller, generally similar to thosedisclosed herein.

U.S. Pat. No. 3,574,301, issued Apr. 13, 1971, to J. S. Bernharddiscloses a segmented bias roll to enable different biases and differentfunctions to occur at different areas of the roll'circumference.However, this bias roll is in a developer station rather than a transferstation. v

U.S. Pat. No. 3,647,292, issued Mar. 7, 1972, to D.

J. Weikel, J r., discloses a uniform transfer belt system for carrying acopy sheet through the transfer station, vacuum means for holding thesheet on the belt, and transfer field generating means, which in oneembodiment includes multiplestationary transfer electrodes in astationary segmentedplate with different (increasing) appliedpotentialsacting at the back of the transfer belt.

U.S. Pat. No. 3,644,034, issued Feb. 22, 1972, to R. L. Nelson,discloses a segmented wide conductive strip transfer belt to which twodifferent bias potentials are applied by two support rollers to thosesegments passing over the rollers. The conductive segments are separatedby 1/16 inch insulative segments.

The transfer system of the invention may be utilized in any desiredpath, orientation or. configuration. It may be utilized for transferwithan imaging surface of any desired configuration, including either acylinder or a belt. Photoconductive belt imaging surfaces inelectrographic copying systems are exemplified by U.S. Pat. Nos.3,093,039; 3,697,285; 3,707,138; 3,713,821, and

and details whereby the above-mentioned aspects of the invention areattained. Accordingly, the invention will be better understood byreference to the following description and to the drawing forming a partthereof, wherein:

The FlGURE is an axial cross-sectional view of an exemplary duplextransfer copying system in accordance with the present invention.

Referring to the FIGURE, there is shown therein an electrostatic duplexcopying system as one example of the present invention. The system 10here comprises a transfer rnember 12 in the form of a cylindricalroller. The outer or image receiving surface '14 of thetransfer member12 resiliently engages the imaging surface 16 of a conventionalphotoreceptor 18 at a transfer nip 20.

In the transfer nip 20, the transfer of the two image patterns of tonerparticles 22 to the opposite sides of a copy sheet 24 is accomplishedsimultaneously. Both toner images may be conventionally xerographicallyformed and developed on the photoreceptor 18 imaging surface 16.

In the system 10 a first imagewise pattern of the toner 22 is firsttransferred from the photoreceptor imaging surface l6 onto the imagereceiving surface 14 of the transfer member 12 in the transfer nip 20,inthe absence of the copy sheet 24. The first toner image is therebytemporarily retained on the image receiving surface 14 and therebyrotated around on the transfer roller 12 fora subsequent transfer to theupper surface of the'copy sheet 24, which has then been'inserted in thenip 20. A second toner image formed on the photoreceptor 18 imagingsurface 16 is then transferred directly from the imaging surface 16 tothe facing lower surface of the copy sheet 24. I I

It may be seen that the image receiving surface ,14 of the transfermember 12 functions as-an intermediate image supporting surface, andthat twotransfers of this first image are required, the second of whichoccurs simultaneously with the single transfer of the second image. Allimage transfers are effected by electrical, transfer biases applied tothe transfer member 12 to form transfer fields between the imagereceiving surface 14 i and the imaging surface 16 at the transfer nip20.

For the transfer to opposite sides of the copy sheet 24 simultaneouslyin the transfer nip 20, the first toner im-' age, stored on theimagereceiving surface 14, has its charge polarity reversed prior toretransfer tothe copy sheet 24, so thatthis first imagewill transfer inthe opposite direction from thesecond image, i.e., be repelled from theimage receiving surface 14 rather than attracted toward it. Thispolarity reversal of the first toner image is provided by a coronacharging system 26 operated to provide D.C. ion emissions charging thefirst image at a charging. area which is substantially spaced from thetransfer nip 20. The corona charging system 26 provides ion emissionsopposite in polarity from the initial toner charge as the toner passesunder the corona output on the image receiving'surface 14.

' Further details and descriptive material in regard to theabove-described structure and function may be- 34. The conductors 34extend axially through the transfer member 12 in a parallel, closelyspaced apart relationship, closely underlying the image receivingsurface A conventional transfer bias supply 36 is operatively connectedto selected ones of the conductive strips 34 only adjacent the transfernip 20 bya fixed electrical sliding contactor 38. Only one bias supply36 and contactor 38 are shown. However, it will be appreciated that, asdescribed in the above-cited Schmidlin U.S. Pat. No. 3,684,364, multiplecontacts and bias potentials may be utilized for transfer fieldtailoring.

The individual conductors 34 are illustrated here for drawing clarity asscaled exaggeratedly wide in comparison to the transfer member 12 andthe transfer nip 20. In an actual preferred structure the number ofconductors would be much greater and a much smaller spacing would beprovided therebetween. Twenty or more conductors 34 per centimeter arepreferable so as to avoid any possibility of a printout of fringe fieldchargepatterns or other visible defects in the transferred image. Itwill also be appreciated that although the transfer member 12 is hereillustrated as a roll cylinder it could also be in the form of anendless flexible belt.

it will be appreciated that for higher transfer fields with lowervoltages applied to theconductors 34, that the roll outer layer 32 should'be quitethin if it comprises a dielectric layer, for example, 0.1millimeters. However, if the roll outer layer is relaxable(semiconductive), so that transfer charges are conducted out to theouter surface 14, then it will be appreciated that this roll outer layermay be substantially thicker. It may also be desirable to have theconductors be sufficiently flexible so as not to interfere with thedesired roll duror'neter.

While the interior of the transfer roll 12 is illustrated here as hollowfor clarity, it will be appreicated that it may be partially or fullyfilled with a suitable solid or resistive material, providin that theindividual conductors 34 are not shorte together. The electricalcontacts with the conductors 34 by the transfer contactor 38 and thegrounding brush 39 can be at any location, such as internallycircumferentially at one end of the roll as shown, or at an outsidesurface in a radial plane if the conductors are;brought out onto a rollend.

Referring now to the corpna charging system 26, this comprises analternating c rrent power supply 40, a direct current power supply,- 42,and a switch 44 alternately connecting one of tpese two power supplies40 or 42 to a conventional corotron 46 which is spaced over the imagereceiving surface 14 man image charging area substantially spaced fromthe transfer nip 20. A grounding brush 39 makes. an electrical groundingconnection with all of the donductors 34 underlying the image receivingsurface 14 in this same charging area,

i I When the switch 26 conhectsthe conventional D.C.

corotron supply 42 to the corotron46, the previously described imagepolarity/reversal is provided by ion emission from the corotron 46 ontothe image receiving surface 14, including the toner 22 thereon. When theswitch 26 is alternately switched to connect trie corotron 46 to theconventional A.C. supply 40, an alternating polarity ion emission outputis provided therefrom for charge neutralization of the underlyingsurface 14, including the toner 22. It will be appreciated, of course,that two separate alternately activated corotrons could be utilizedinstead, if desired, rather than switching only the input to a singlecorotron as disclosed here. The actuation of the switch 44 is preferablyautomatic, in coordination with the movement of the transfer member 12.That is, during the initial rotation of the transfer member 12 in whichthe first toner image is being placed on the surface 14 for subsequentretransfer, the DC. supply 42 will be connected for polarity reversal ofthis image. Then after this first toner image begins to retransfer tothe copy sheet 24, the switch 44 is preferably switched automatically inresponse to the further rotation of the transfer member 12 (or othersystem components) to electrically neutralize the remaining(untransferred) toner particles on the image receiving surface 14 sothat they may be removed at a cleaning station.

Cleaning of the A.C. neutralized toner particles from the imagereceiving surface 14 of the transfer member 12 may be accomplished byany conventional toner cleaning means, such as a blade, web, or brushsystem. A conventional xerographic cleaning brush 50 is illustrated herein rotational sweeping cleaning engagement with the surface 14 oppositefrom the transfer nip 20. This cleaning brush 50 is pivotally mountedhere on a lever arm connected to a solenoid 52, for periodicallypivotally lifting the cleaning brush 50 away from the surface 14. Thisbrush 50 disengagement allows the first toner image transferred to passthis cleaning station without being disturbed prior to its retransfer.It will be noted that the grounding brush 39 preferably extends intothis cleaning area for grounding the conductors 34 in this region.Thisprevents any charges from being maintained on the conductors 34adjacent the cleaning brush'50 which might resist removal of toner bythe cleaning brush.

The grounding brush 39, together with the discrete conductors 34,provides complete electrical isolation of the toner charging ordischarging, the toner'cleaning, and the toner transfer functions inthis system 10. As noted, the grounding brush or contactor 39 groundsall of the conductors 34 adjacent both the charging system 26 and thecleaning brush 50. This electrically grounds any charges which wouldotherwise be retained on the conductors 34 from the transfer bias supply36. lt also provides, in effect, one (grounded) plate of a capacitorformed between the charges on the surface 14 and the conductors 34 inthe charging area. This considerably increases the charge density whichmay be applied by the charging system 26, as well as stabilizing thevoltage reference level so as to avoid any random charge effects on thesubsequent transfer. More complete A.C. charge neutralization may alsobe provided for the same reasons. Further, with this system no transferbias charges or transfer fields can be present in the charging area.Such transfer charges could otherwise resist the reversal chargingoutput of the charging system 26, since the polarity of the DC. supply42 (and the connected corotron 46 output) is the same as that of theapplied transfer bias, The transfer field level may be set independentlyby adjustment of the bias supply 36, and the output of the corotron 46may be set independently by adjustment ofits D.C. supply 42, without anypossible mutual interference due to conduction through, or chargetransfer with, the transfer member 12.

The electrostatographic duplex copying system disclosed herein ispresently considered to be preferred; however, it is contemplated thatfurther variations and modifications within the purview of those skilledin the art can be made herein. The following claims are intended tocover all such variations and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In an electrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member and then issubsequently retransferred to a final support surface at a transfer nip,and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and amultiplicity of electrically discrete conductive strips underlying saidimage receiving surface;

transfer bias means for applying an electrical transfer bias to selectedones of said conductive strips only adjacent said transfer nip for saidimage transfer to said final support surface; and

selectively operable image charging means for selectively applying anelectrical charge to said image receiving surface of said transfermember, at a charging area of said surface substantially spaced awayfrom said transfer nip, independently of said transfer bias means;wherein said image charging means includes A.C. and DC corona chargingmeans and switching means for switching between said A.C. and.D.C.corona charging means in coordination with movement of said transfermember; where said D.C. corona charging means is for po- 1 larityreversal of said one image and said A.C. corona charging means is forcharge neutralizing.

2. The electrostatographic system of claim 1 further including grounding,meansfor grounding a selected number of said conductive strips whichare adjacent said corona charging means.

3. In an electrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member and then issubsequently retransferred to a final support surface at a transfer nip,

and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and amultiplicity of electrically discrete conductive strips underlying saidimage receiving surface;

transfer bias means for applying an electrical transfer bias to selectedones of said conductive strips only adjacent said transfer nip for saidimage transfer to said final support surface; and

selectively operable imaging charging means for selectively applying anelectrical charge to said image receiving surface of said transfermember, at a charging area of said surface substantially spaced awayfrom said transfer nip, independently of said transfer bias means;wherein said image charging 7 means comprises a single corona chargingapparatus and AC. and DC corona power supplies and switch means forselectively connecting said corona power supplies for selecting betweenimage polarity reversal and charge neutralizing in coordination withmovement of said transfer member. 4. In an electrostatographic duplexcopying system, wherein one image is transferred from an imaging surfaceto a transfer member and then is subsequently retransferred to a finalsupport surface at a transfer nip, and wherein another image istransferred from an imaging surface to said same final support surfaceby said same transfer member:

wherein said transfer member has an image receiving surface and amultiplicity of electrically discrete conductive strips underlying saidimage receiving surface; transfer bias means for applying an electricaltransfer bias to selected ones of said conductive strips only adjacentsaid transfer nip for said image transfer to said final support surface;and selectively operable image charging, means for selectively applyingan electrical charge to said image receiving surface of said transfermember, at a charging area of said surface substantially spaced awayfrom said transfer nip, independently of said transfer bias means;further including grounding means for grounding a selected member ofsaid conductive strips which are adjacent said image charging means. I5. In an electrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member. and then issubsequently retransferred to a final support surface at a transfer nip,and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member:

wherein said transfer member has an image receiving surface and amultiplicity of electrically discrete conductive strips underlying saidimage receiving surface;

transfer bias means for applying an electrical transfer bias to selectedones of said conductive strips only tively applying an electrical chargeto said image receiving surface of said transfer member, at a chargingarea of said surface substantially spaced away from said transfernip,.independently of said transfer bias. means; wherein said imagescomprise charged toner particles, and further including cleaning meanssubstantially spaced away from said transfer nip forcleaning said imagereceiving surface and grounding means for grounding conductive stripswhich are adjacent said cleaning means and adjacent said image chargingmeans.

6. In an electrostatographic duplex copying system,

wherein one image is transferred from an imaging surface to a transfermember and then is subsequently retransferred to a final support surfaceat a transfer nip, and wherein another image is transferred from-animaging surface to said same final support surface by said same transfermember:

wherein said transfer member has an image receiving surface and amultiplicity of electrically discrete conductive strips underlying saidimage receiving surface; transfer bias means for applying-an electricaltransfer bias to .selected ones of said conductive strips only adjacentsaid transfer nip for said image transfer to said final support surface;and r selectively operable image charging means for selectively applyingan electrical charge to said image receiving surface of said transfermember, at a charging area of said surface substantially spaced awayfrom said transfer nip, independently of said transfer bias means;wherein said image charging means includes A.C. and DC. corona chargingmeans and switching means forswitching between said A.C. and DC. coronacharging means in coordination with movementrof said transfer member,where said D.C. corona charging means is for polarity reversal of saidone image and said A.C. co-

rona charging means is for charge neutralizing,

1. In an electrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member and then issubsequently retransferred to a final support surface at a transfer nip,and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member: wherein saidtransfer member has an image receiving surface and a multiplicity ofelectrically discrete conductive strips underlying said image receivingsurface; transfer bias means for applying an electrical transfer bias toselected ones of said conductive strips only adjacent said transfer nipfor said image transfer to said final support surface; anD selectivelyoperable image charging means for selectively applying an electricalcharge to said image receiving surface of said transfer member, at acharging area of said surface substantially spaced away from saidtransfer nip, independently of said transfer bias means; wherein saidimage charging means includes A.C. and D.C. corona charging means andswitching means for switching between said A.C. and D.C. corona chargingmeans in coordination with movement of said transfer member; where saidD.C. corona charging means is for polarity reversal of said one imageand said A.C. corona charging means is for charge neutralizing.
 2. Theelectrostatographic system of claim 1 further including grounding meansfor grounding a selected number of said conductive strips which areadjacent said corona charging means.
 3. In an electrostatographic duplexcopying system, wherein one image is transferred from an imaging surfaceto a transfer member and then is subsequently retransferred to a finalsupport surface at a transfer nip, and wherein another image istransferred from an imaging surface to said same final support surfaceby said same transfer member: wherein said transfer member has an imagereceiving surface and a multiplicity of electrically discrete conductivestrips underlying said image receiving surface; transfer bias means forapplying an electrical transfer bias to selected ones of said conductivestrips only adjacent said transfer nip for said image transfer to saidfinal support surface; and selectively operable imaging charging meansfor selectively applying an electrical charge to said image receivingsurface of said transfer member, at a charging area of said surfacesubstantially spaced away from said transfer nip, independently of saidtransfer bias means; wherein said image charging means comprises asingle corona charging apparatus and A.C. and D.C. corona power suppliesand switch means for selectively connecting said corona power suppliesfor selecting between image polarity reversal and charge neutralizing incoordination with movement of said transfer member.
 4. In anelectrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member and then issubsequently retransferred to a final support surface at a transfer nip,and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member: wherein saidtransfer member has an image receiving surface and a multiplicity ofelectrically discrete conductive strips underlying said image receivingsurface; transfer bias means for applying an electrical transfer bias toselected ones of said conductive strips only adjacent said transfer nipfor said image transfer to said final support surface; and selectivelyoperable image charging means for selectively applying an electricalcharge to said image receiving surface of said transfer member, at acharging area of said surface substantially spaced away from saidtransfer nip, independently of said transfer bias means; furtherincluding grounding means for grounding a selected member of saidconductive strips which are adjacent said image charging means.
 5. In anelectrostatographic duplex copying system, wherein one image istransferred from an imaging surface to a transfer member and then issubsequently retransferred to a final support surface at a transfer nip,and wherein another image is transferred from an imaging surface to saidsame final support surface by said same transfer member: wherein saidtransfer member has an image receiving surface and a multiplicity ofelectrically discrete conductive strips underlying said image receivingsurface; transfer bias means for applying an electrical transfer bias toselected ones of said conductive strips only adjacent said transfer nipfor said image transfer to said final support surface; and selectivelyoperable image charging meanS for selectively applying an electricalcharge to said image receiving surface of said transfer member, at acharging area of said surface substantially spaced away from saidtransfer nip, independently of said transfer bias means; wherein saidimages comprise charged toner particles, and further including cleaningmeans substantially spaced away from said transfer nip for cleaning saidimage receiving surface and grounding means for grounding conductivestrips which are adjacent said cleaning means and adjacent said imagecharging means.
 6. In an electrostatographic duplex copying system,wherein one image is transferred from an imaging surface to a transfermember and then is subsequently retransferred to a final support surfaceat a transfer nip, and wherein another image is transferred from animaging surface to said same final support surface by said same transfermember: wherein said transfer member has an image receiving surface anda multiplicity of electrically discrete conductive strips underlyingsaid image receiving surface; transfer bias means for applying anelectrical transfer bias to selected ones of said conductive strips onlyadjacent said transfer nip for said image transfer to said final supportsurface; and selectively operable image charging means for selectivelyapplying an electrical charge to said image receiving surface of saidtransfer member, at a charging area of said surface substantially spacedaway from said transfer nip, independently of said transfer bias means;wherein said image charging means includes A.C. and D.C. corona chargingmeans and switching means for switching between said A.C. and D.C.corona charging means in coordination with movement of said transfermember, where said D.C. corona charging means is for polarity reversalof said one image and said A.C. corona charging means is for chargeneutralizing, wherein said one image comprises charged toner particles;and further including cleaning means substantially spaced away from saidtransfer nip for cleaning said image receiving surface and groundingmeans for grounding conductive strips which are adjacent said cleaningmeans and also for grounding conductive strips which are adjacent saidcorona charging means.